TC Main Shaft Lubrication

[cham]

Hope you all are well,

So what’s the deal with the All-Mode ATX T-case pump.  Seems a while ago someone found out through the FSM that the “Main Shaft” rotates a pump in the T-case that lubricated the T-case while driving.  Sounds like someone confused the “main shaft” for the front shaft and assumed manual locking hubs would not work for that reason.  But then it was decided that the “main shaft” in the FSM is actually referring to the rear drive shaft; can anyone confirm this?

 

I’ve replaced my front driveshaft U-joints about a year ago and still get a vibration (and before anybody asks, the vibration did go away initially when I took the front driveshaft off to diagnose).  After getting new tires and a lift it seems worse so I’m planning on taking the front drive shaft off again to diagnose if the vibration goes away.  I’m assuming it should be fine with all of the people running manual locking hubs on their all mode pathys, this essentially replicates that condition (although the cv axles and diff are still spinning).  
 

My plan was to get the front drive shaft balanced if the vibration goes away when I remove it but technically it could still be the cv axles or differential (driveshaft connects the diff to the T-case which could be what transmits the vibration to where I’m sitting). So even if I remove the front shaft and the vibration goes away; could it still definitively not be the driveshaft causing the vibration?

Edited September 1, 2023 by cham

[Slartibartfast]

TF-160 of the '03 manual shows the oil pump on the back of the transfer, accessible by removing the tailshaft housing, geared off the rear output shaft (actually looks like it's running off the speedometer drive gear). Based on that, looks like it should pump regardless of what the front end is doing. And yeah, I'd expect it to behave about the same as unlocked hubs. You might get a light on the dash if the control unit for the transfer gets confused--IIRC some of them determine front wheel speed from the ABS sensors, and some watch a sensor on the front output of the transfer, and the latter system gets understandably confused when it sees what looks like a rolling burnout at highway speed for hours. AFAIK the transfer itself doesn't notice or care.

 

TL;DR, yeah, should be fine.

 

If it doesn't vibrate with the driveshaft out, that points to the driveshaft. I haven't messed with the U joints on mine, but I've heard they can be a PITA to get balanced again afterwards. The PD section of the manual shows a bunch of different thicknesses of snap rings that I assume are used to get the end-play correct. Worth a look if you haven't yet.

 

I remember one case where a guy had a vibration only in 4x which IIRC came down to his front diff bushings being so trashed that the diff was moving and screwing up the U-joint angle when the front end was loaded. Doesn't really match your symptoms, but it's the only other thing I can think of that would cause a front-end vibration that isn't tire wear or bearings or something along those lines. My money's still on the driveshaft.

Edited September 2, 2023 by Slartibartfast

[cham]

Thanks Bart you seem to have the answer to most of my inquires I do appreciate the insight.

 

Yeah it certainly is a pain diagnosing vibrations and at this age throwing parts at the driveline and suspension isn’t necessarily a bad thing.  The front shaft has the annoyingly contrived C style Circlip snap rings instead of the end cap snap rings and is a pain and a half to install without any binding.  I used Spicer Red Box which is the best you can get aftermarket for our front shafts and even after installation the vibration was still there (I replaced them initially not just because of a vibration but a clicking coming from the shaft).  Took a trip to Colorado where I used 4WD a lot (at high speeds too) which seemed to get rid of a lot of the vibration but still remained.  
 

Fast forward to new tires and a lift and now I’ve got a vibration exactly at 50mph and above 70mph that feels kind of cyclic.  It could honestly be my cv axles as the inner boots just tore from the lift and I have no idea as to the condition of my front diff bushings.  I think I’m going to go with the Value Select Nissan CVs as Ive heard so many woes with the aftermarket brands.  I’ll take out the front driveshaft as well and see where I’m at in terms of vibration.  
 

Any experience with value select parts?

[Slartibartfast]

No personal experience. I think I saw someone complain about them being reboxed aftermarket crap on r/justrolledintotheshop, but can't find the post now, and the name is generic enough that I could be confusing it with something else. There was some chatter on the Farcebook group a while ago about aftermarket CVs with a better range of motion than stock, not sure if those are still available. Rebooting is also an option--though the last time I did that, I swore I'd just buy new ones the next time. Good lord those things put up a fight.

 

The vibration getting worse with the lift and tires is interesting. If the vibration's still there with the driveshaft out, and you haven't tried rotating the tires yet, give that a go.

[cham]

Yeah I think I also read something along those lines about the Nissan Value Select being rebadged aftermarket for like a Nissan Altima CV axles.  Regardless it seems all the aftermarket stuff are a crapshoot whether it will bind or not and last.  
 

I know there are some “Extended Travel” options out there now offered by Napa and O,Reily’s etc; is that the extra ROM you were talking about?  I don’t think they’ve been around long enough for anyone to get real opinions of them yet and it seems the same manufacturer is supplying the parts for all of the “extended travel” brands from what I can tell.

 

As for the vibration; maybe my CVs are worn out enough to where the extra lift (MD Springs with Trim Packer) is just enough to make them somewhat bind and cause the vibration.  Most people seem to not have issues with binding though until they’re running like 0.5”-1” spacers on top of stiffer coils.

 

I guess the way I'm seeing it is my original OEM axles are likely 220k old so even rebuilding them with new boots and grease means they are at the end of their life even being the best quality OEM.  I don't even think the original OEM are sold by Nissan anymore; only their Value Advantage Line.  I'm thinking of either going the NVA or O'Reilly's ImportDirect Extended Travel option "NI8185ET" being that many people seemed to be okay with the normal "NI8185" axle.  If I had the funds I'd go with the Napa ET options but at $350 an axle; its considerably more, especially when the design looks identical to the Oreilly's ET and TrakMotive ET designs.  The price difference must be in the materials and manufacturing/quality control.  

Edited September 5, 2023 by cham

[cham]

Removed the front shaft and the vibration at 50mph and above 70mph is much better, but unfortunately still there to some degree.  On the U-joints replaced around a year ago for the front shaft; there is binding in a couple of the cups so its not surprising the vibration got better.  The vibration is still mostly felt in the pedal so my assumption is its the cv axles since installing the lift made the vibration worse.  The only problem is I jacked the front off the ground and when spinning the wheels there was zero binding for both the driver and passenger cv axles. 

 

If a cv axle isn't causing any binding; can it still be the source of a vibration?

(Also I forgot to mention my tires are only a few thousand miles old and I had them rebalanced the other day just to rule that possibility out)

 

Edited September 5, 2023 by cham

[Slartibartfast]

TrakMotive sounds familiar, might've been that one. Didn't know they were $350 each!

 

I haven't heard of CVs vibrating, but if it's not the driveshaft or the tires, I don't know what else it would be. How high is your lift? I've heard of R50s lifted too far without a subframe drop having CV issues.

[cham]

Sorry no the TrakMotive Extended Travel is only about $150 sold on RockAuto but I have read reports of them actually failing.  The Napa version of the Extended Travel design is $350 despite them looking identical to the TrakMotive version so who knows what's actually going on.  I'm assuming the Napa version is made with better materials and tolerances but it could simply just be a huge markup.  

 

I've only got the Medium Duty OME Coils all round and the 3/8" trim packer (Rocky Road Outfitters Spacer) on top up front.  I've read people with more lift and no problems so I'm just going to have to do more investigation.  Any chance I might be able to remove my cv axles and drive with out them?  Since the wheel bearings are preloaded on the steering knuckle stub axle; removing the cv shouldn't effect that I'd assume. 

[R50JR]

3 hours ago, cham said:

Sorry no the TrakMotive Extended Travel is only about $150 sold on RockAuto but I have read reports of them actually failing.  The Napa version of the Extended Travel design is $350 despite them looking identical to the TrakMotive version so who knows what's actually going on.  I'm assuming the Napa version is made with better materials and tolerances but it could simply just be a huge markup.  

 

I've only got the Medium Duty OME Coils all round and the 3/8" trim packer (Rocky Road Outfitters Spacer) on top up front.  I've read people with more lift and no problems so I'm just going to have to do more investigation.  Any chance I might be able to remove my cv axles and drive with out them?  Since the wheel bearings are preloaded on the steering knuckle stub axle; removing the cv shouldn't effect that I'd assume. 

It's been a while....I'll chime in with what little I know.

 

The auto transfer case still spins the front driveshaft even if the hubs are unlocked. The vibration could be caused by this on your vehicle.

 

The best CV axles are OEM as they have the greatest operating angle. 

 

The Napa axles are rebadged Tracmotive. I've also read about them failing.

 

Do you have VDC on your model? I believe the model with traction control uses the abs tone ring for more than abs, so you may have issues with that (if vdc)

 

 

[cham]

Was VDC the traction control system that was supposed to mimic lockers?  I believe 03 and 04 MY are the only years to get it of the R50 generation.  To my knowledge I do not have it as I can spin my wheels pretty easily if I get crossed up when crawling. 

 

I'm going to go with the Value Advantage and see how it goes.  I'll check for binding immediately after installation at full droop before I put any miles on them as well.  The warranty is only for a year but it seems like a no questions asked type deal unlike some of the parts store special stuff.  Plus I probably won't be with this rig but so much longer. 

 

I'm also guessing even if these are rebadged aftermarket I would think Nissan would have the forethought to heighten its quality control on what they allow to be sold under their name unlike most aftermarket parts stores.  Lastly these should be as close to the original OEM axles in terms of dimensions, so I would think getting those Rockford Dura Thermoplastic Boots would fit no problem if ever need be.  Couldn't say the same for the "Extended Travel" offerings which I seem to be hearing a lot of boot failures with normal driving.  

 

As for the remaining vibration its only barely noticeable now without my front driveshaft in so my guess is its a combination of my front CVs being worn out and my rear driveshaft U-joints also beginning to show their age.  I mean even with the front shaft not seeing constant torque like the rear; those factory u-joint needle bearings had been churned into dust when I disassembled them; I can only imagine what the rear look like at this age.  

Edited September 7, 2023 by cham

[Slartibartfast]

The wheel bearings will work without the axles, but the axles seal the back side of the wheel bearing to hold the grease in, so I wouldn't leave it like that for long. Probably fine for a test drive, though.

 

The VDC/traction control system was the difference between the two systems I mentioned earlier. I do not remember which was which, just that it was backwards of how I expected it to be.

[cham]

That’s right; that rear grease seal will have a gaping hole for grit ingress. I think for that reason Im just going to swap the axles and forgo that test all together.

So I also decided to order the front “final drive” differential side axle seals as the axle end seam behind my passenger side cv axle is leaking gear oil. This includes a grease seal and oil seal. So I’m looking at the FSM and it’s not making any real sense on how to remove the side end axle for the the front diff.





As you can see in the photos it shows removing it with a mallet and then later shows hammering off some collar and then using a slide hammer to remove the side axle but it was already removed with the mallet. Confused if it’s just showing multiple ways to do it; also what’s with hammering a collar off? I was thinking of just using a rubber mallet for disassembly and installation. Concerned though about what the collar’s purpose is.


Sent from my iPhone using Tapatalk

[Slartibartfast]

Usual disclaimer, I haven't had an R200A apart. But I had a look at the manual, and here's how I think it goes.

 

The first time, you're removing the long-side axle shaft, the bearing, and the flange that holds the bearing (labelled "extension tube retainer" on PD-18) all together. While it's out, you cut the collar which (I'm guessing) holds the bearing in place on the axle shaft. Then you bolt the extension tube retainer back to the axle tube to hold it (and the bearing) while you draw the axle out of the bearing with the slide hammer.

 

I don't know why they have you bolt it back up rather than using a bearing splitter and a press. It could be that it comes out easily enough with the slide hammer that setting up the press would be an unnecessary hassle, or maybe they thought the extension tube retainer might break if it wasn't bolted down in four places while it got yanked on.

 

 

[cham]

Ah I see now; the side axle comes out with the extension tube retainer, bearing, and grease seal still attached.  If I wanted to get at that grease seal I’d need to cut the collar and do exactly as the FSM states with the slide hammer.  Don’t trust myself on that one with a “cold chisel” so I guess I’m only replacing the oil seal now.  
 

I would think that the oil seal is what is leaking the majority of the gear oil whereas the grease seal just protects the axle shaft bearing.  Any reason you think it’s absolutely necessary to take the extra step and cut the collar? For example maybe the gear oil has contaminated the axle shaft bearing and now I need to degrease and re-grease the bearing etc etc

[Slartibartfast]

If gear oil is leaking from between the extension tube retainer and the tube, then yeah, sounds like it's just the inner seal that's gone, and the bearing might still have grease in it. If gear oil is coming out of the grease seal, that suggests the grease seal is bad too--and the oil had to go through the bearing to get there, so the grease is contaminated/washed out. If the grease is gone, then the only thing keeping the bearing alive is the oil leaking into it, which new inner seals will cut off. Unless you can clean and regrease the bearing in place, and you trust the outer seal to hold that grease, I'd say go for the whole meal deal here so you only have to drop the diff once.

 

A cold chisel is just a stout blunt chisel, as opposed to the sharp chisels used in woodworking. A screwdriver would probably work, depending on what the collar is made from. You're not beating on a bearing or sealing surface, so I wouldn't worry if you scuff it. So long as the shaft is well supported below where you're hammering so you're not trying to bend it, and you don't go after it with a grinder or an air chisel or something, I think you would struggle to hurt it.

[cham]

Yeah I think you’re right on the money. That inner oil seal is definitely failed as the gear oil is what I’m seeing leak at that seam. It remains to be seen whether the grease seal is also failed or not; let’s hope the grease seal is made of the same class of polymer or something similar that’s resistant to gear oils otherwise the oil might be eating away at it once it made contact.

I’ve also heard (at least for wheel bearings) some people let their axles leak into the wheel bearings and give them a gear oil bath; I think it’s mainly done on 80 series and 100 series land cruisers if I remember correctly because the axles leak so much. Obviously a diff axle and hub wheel bearing assembly are different but I believe in our case both are the tapered style bearings.

Theres also the possibility even if I see oil leaking past the front side of the grease seal it’s not the end of the world as it was only meant to hold grease back and something like gear oil being less viscous might be able to leak past pretty easily. I think what I’ll try to do is check the condition of the grease seal and with the side axle removed, try to lubricate the backside of that axle bearing if there is an opening to do so. I’m worried about degreasing it when I’m not actually cutting the collar and removing the bearing. If I can only get grease at it from one side I likely won’t be re-greasing the entire internals of the bearing. So supplemental grease without degreasing would be ideal in my eyes.

Unfortunately a cold chisel, slide hammer, and axle press for the new collar are not apart of my toolset and I would be worried about screwing it up if I tried and alternative tool on such a crucial component.


Also I might have confused you with the FSM, I’m not dropping the diff just getting at those seals since I will have my CV axles off when replacing them. From what I can tell there the side axle should come right out without needing to open the diff case up at all. It’s just those bolts holding the extension retainer on.


Sent from my iPhone using Tapatalk

[Slartibartfast]

Some axles don't have greased bearings--the bearings are lubed by gear oil by design. I'd be surprised if the rubber in a grease/oil seal could handle one but not the other.

 

I bought a press when I did my rear bearings, and ended up having to make a spline nut wrench and some press tooling from scratch. There's usually a workaround, but I don't blame you for not wanting to break it down more than you have to. Hopefully the grease isn't too washed out and you can just shoot some in. I think I've seen a grease gun adapter that's basically just a zerk and a needle--one of those might let you get into the bearing better.

 

And yeah, no sense dropping the diff if you can avoid it! It's a big awkward chungus of a thing. A friend of mine did the seals on the front diff in his S10 with the diff in place, though those were not nearly as complicated.

[cham]

That’s right I believe a lot of Semi trucks have their axle bearings bathed in gear oil rather than grease.

Funny enough I actually do have that needle zerk adapter in the form of this Mountain Bike Park Tool lol, I was thinking this would work pretty well vs my normal grease gun.

I did actually notice around the same time my rear axle oil seals are also leaking but only very very slightly, almost unnoticeable. At the same time, that means it’s probably the best time to replace the oil seals before the gear oil washes out the bearing grease and ruins them.

Sent from my iPhone using Tapatalk

[Slartibartfast]

It's not just semis! I haven't had enough rear axles apart to say for sure, but I suspect our greased bearings are more the exception than the rule, at least on older stuff.

 

That Park greaser looks like a great way to go. Much easier to maneuver.

[cham]

How does the ATX14A T-case transfer power in the Auto setting?  I think I read it doesn't just send power to the front axle when slip is detected but also progressively the more you accelerate.  Sounds like it might use a "viscous clutch pack" instead of a viscous coupling which I believe are slightly different.  So theoretically if one wheel slips not all power is siphoned to that one wheel. This would happen in a a fully mechanical center differential like found in early 80 series LCs before they started adding a viscous coupling.  Also when you lock the transfer-case in 4H, are you actually "locking" it per say or is it just spinning up that viscous clutch pack to "mimic" a locked center differential when in reality nothing is actually "locking" the front and rear driveshafts, its just a lot of friction in the clutch packs holding the shafts at similar RPMs?

Edited September 14, 2023 by cham

[Slartibartfast]

There is no center diff or viscous anything. The ATX14A is a part-time transfer case, so the rear output is always driven directly (1:1 off the transmission, or 2.596:1 in low range). The front output is coupled to the rear output using a wet clutch, like you'd find in an automatic transmission. The clutch is controlled by a computer. In 4H or 4L, the clutch engages fully, locking the front driveshaft to the same speed as the rear one--which is fine off-road, but usually not what you want on pavement. In auto mode, the computer feathers the clutch as needed, squeezing it together harder the more the rear wheels are slipping, the harder you're accelerating, or the more you're engine braking. TF-45 of the service manual has a cartoon explanation of this.

 

Because there is no center diff, there is no risk of all the motion going to one wheel (unless you're in 2H)--but no center diff is also why you get torque bind on grippy surfaces in 4x (also, why you shouldn't drive on grippy surfaces in 4x). This is why auto mode exists. It only grabs the clutch as hard as it has to to keep you going, so you can drive it on dry pavement without torque bind, but if you do find a slick spot, the front end will still pull you through.

 

Basically, they added an all-wheel-drive setting to a part-time transfer case, and all it cost them was one more computer, two hydraulic pumps, and five times as many pages in the service manual. Seriously, the TX10A takes up 30 pages, and the ATX14A takes up 154. It's a neat piece of kit, but good lord is it complicated. They do seem pretty reliable, though, and I'm told the auto mode is nice in patchy snow.

[cham]

Thanks for the page reference I’ll check that out for sure. So I’m still a little confused about the whole “wet clutch” thing because wouldn’t that be the same as a viscous clutch pack? Is it a derivative of a multiplate clutch like the Nissan GTR Atessa system uses?

So I get how the system is electronically modulating the clutch engagement in Auto. So what if you’re applying power into a corner; does it separate the clutches to allow the front wheels to spin faster than the rear or will it still slightly engage the clutches to transmit power to the front wheels since you are “accelerating” but also allows slip of the clutch so that there isn’t any binding. A center differential in the end can achieve the same thing; you just lock the diff and the front and rear driveshaft are locked at a 50:50 distribution and in fact I would claim it’s a stronger system since it’s actually locking bevel and pinion gears together with a pin instead of a wet clutch. The problem is when it’s unlocked, only one wheel needs to loose traction for the entire thing to lose forward momentum unless there is some addition engineering aid i.e. viscous coupling or multiplate clutch or electronic wizardry.

So when we are in 4H the wet clutch is fully “locked” as you say but is it actually locked or just held together through friction of the plates and can still potentially slip?


Edit: Yikes just saw the T-case oil filter service in the manual. It’s $230! Any chance you might be able to just remove it and clean it and throw it back in? At this age should we replace it haha my T-case does produce a little bit of a whine now days.

Sent from my iPhone using Tapatalk

[Slartibartfast]

Wet clutches are controllable, viscous couplings are not.

 

Viscous couplings are just a stack of plates with thick oil between them that makes it hard for them to move one independent of the other. Half of the plates go to the input, half to the output, alternating, so when the coupling is forced to slip, all the oil across all the surface area of each of the plates (except the two on the ends) fights it. The wiki writeup on them says the oil gets thicker the more it heats up, so the more you beat on it and force it to slip, the harder it fights back. It's got enough slip to avoid torque bind, but it fights back enough to put power down when you need it. It has no external controls.

 

A wet clutch is more like the clutch in a manual transmission vehicle (except that it's soaked with oil). An external force (in this case fluid pressure on a piston, supplied by the pumps, controlled by the computer) clamps the plates together, causing friction between them. Clamp them hard enough and they don't slip at all. It's the same tech that grabs gears in automatic transmissions, and I think it's common in motorbikes and quads, too. Usually they've got a bunch of plates, like the multiplate clutches used in some sports cars, though the exploded diagram for the ATX14A shows a smaller number of plates than I would've expected. Technically the wet clutch could slip when clamped completely up, same as a dry clutch, but I imagine you'd have to hit it pretty damn hard to break the static friction unless it was wore slap out or you were hitting it with way more power than it was designed to take.

 

AFAIK auto mode won't lock the clutch completely, so no, it shouldn't torque-bind if you're gassing it through a corner.

 

The viscous is a far simpler solution, but I imagine it did not play well with the ABS/traction control, or Nissan didn't like its road manners (might be more prone to understeer). The computer-controlled-clutch solution meant they could make it behave however they wanted. I've seen similar computer-controlled wet-clutch transfers in domestics of the same era (BW4405 in an Exploder, NP236 in an S10 Blazer), so it wasn't just a Nissan thing.

 

That is a lot for a filter. If you haven't, google the Nissan part #--if that quote came from a dealer, you may find it cheaper online. If it's like the filter for the trans, it may be more of a screen than a filter, and easy enough to clean out. Worst case, I imagine the transfer case would have to be absolutely shredded to shed enough material to clog the filter.

 

New fluid is a good idea, though. Did a world of good for the TX10A in my '95. Make sure you get the right stuff!

[cham]

I see I was just confusing viscous for meaning wet for the clutch packs.  I know how a viscous coupling works since they are pretty cool mechanical marvels.  The fluid is shear-thickening so non-Newtonian and when used in tandem with a center diff, if the driveshafts experience a differential in RPMs the fluid induces a lot of friction and tension in the housing as the alternating plates spin past each-other but there is no "clamping" force with a spring, the fluid creates all of the friction between the driveshafts.  What's interesting is when taking corners the required difference in driveshaft speeds is marginal and not enough to really engage the coupling which prevents wind up so its a perfect solution right?!  Well I think the main drawback with them is they can have a propensity to lock up over the years and they also can have a delay in engagement but depends on the system and whatnot.  Some manufacturers make them have a more aggressive engagement while others make them softer which aids in delaying their engagement.  So much so that some manufacturers I think VW Sycros system literally preload the viscous coupling for faster engagement but at the cost of wearing tires faster from sometimes excess tension in the drivetrain.  

 

I think I was applying the mechanical nature of the viscous coupling to the multi-plate system which doesn't makes sense since the wet multi-plate clutch doesn't have a mechanical reactive nature like you said; it needs to be told by a computer exactly what to do.  The nature of the viscous coupling is completely reactive based on the properties of the dilatant, so i guess I should say hydro-mechanical nature.

 

What I'm still trying to conceptualize is how either system can simultaneously apply torque/power while still allowing slip (so gassing it into a corner; or slip occurs while gassing it).  In one scenario, you want there to be slip to keep from windup, in the other you want the slip to stop.  So for the wet, multiplate clutch (which is what the manual calls it), since it's like a manual clutch in a trans, you wouldn't simultaneously apply slight clutch pressure and then give it gas because that would just wear the friction material.  When you down shift you rev match but that's literally to get the two shafts spinning the same speed or close enough.

 

I guess I can only think of it as locked or unlocked in my head.  Could it be doing just that; slip lock slip lock but just at insanely fast intervals?  Or is it more likely the plates are constantly slipping past each other but even that slipping has friction between it thus transmitting torque and power?

 

 

Edit:

This guy makes the claim that the All-mode is essentially switching the transfercase into 4 HI when slip occurs and its just constantly going back and forth between 2H and 4H to prevent driveline binding/wind-up.  Sounds like they don't know that power is sent to the front in other conditions such as when applying more gas.  They could still be right though as the system watches wheel speed sensors so if it detects the front axle wheels spinning faster than the rear axle wheels; it might switch back to 2WD in that moment.  That would solve my confusion about simultaneous torque delivery and slip when gassing it into a corner; because that would mean its just in 2WD in that scenario.  

 

Link to forum thread:

https://forums.nicoclub.com/auto-mode-always-4wd-t548182.html

 

 

Edited September 15, 2023 by cham

[Slartibartfast]

Based on the cartoon in the manual, I still think it's dragging the clutch to transmit only as much torque as it thinks it needs to. Think of it like brakes--they're not just on or off. Slipping a clutch like that does seem a little abusive, but automatic transmissions slip a little whenever they grab a gear (or they'd slam you around), and the clutches in a limited slip diff are slipping any time you're not going dead straight. They're built to take it, and also they're not slipping all that fast, or for all that long.

 

In normal operation, I would not expect the transfer case clutch to have to slip all that much, either. If the system kicks in quick enough in response to wheel slip, there won't be that much speed difference to correct for, and the slippage when cornering shouldn't be much either (similar to how it's not enough to activate the viscous coupling). Driving down the road with mismatched tires may be a different story, if the transfer gets confused and drags the clutch for miles on end trying to correct what it would see as wheel slip. Hopefully the same code that makes the computer pissy about manual hubs would catch on to what was happening and release the clutch before it burned itself out--or the operator would know enough to not leave it in auto mode when running an undersized spare.

 

I imagine the computer is pulse width modulating the solenoid (cycling it on and off faster than the clutch can react to, while varying the length of the 'on' pulses) to dial in whatever pressure it wants. (IIRC this is also how the automatic transmission controls its line pressure.) If it was just stabbing the clutch to full lock, letting off to see if that fixed the slip condition, then stabbing it again if it didn't, I would expect the truck to shudder like the ABS was kicking in.

 

I have no personal experience with this box, so I'm mostly speculating here--as are the people in the thread you linked. If you want to take a deep drive into how this critter operates, the TF section in the service manual is your best and probably only source of accurate information, short of dissecting yours to see what makes it tick, or datalogging the solenoid in action.

 

My old TX10A may be clunky and primitive, but it sure is easier to understand!